A color filter method and a field sequential method are known as display methods for liquid crystal display devices. In a liquid crystal display device in which images are displayed by a color filter method, a plurality of subpixels each having a color filter that only transmits light with a wavelength of a given color (e.g., red (R), green (G), or blue (B)) are provided in each pixel. A desired color is produced in such a manner that transmission of white light is controlled in each subpixel and a plurality of colors are mixed in each pixel. On the other hand, in a liquid crystal display device in which images are displayed by a field sequential method, a plurality of light sources that emit lights of different colors (e.g., red (R), green (G), and blue (B)) are provided. A desired color is expressed in such a manner that the plurality of light sources that emit lights of different colors repeatedly blinks and transmission of light of each color is controlled in each pixel. In other words, according to the color filter method, a desired color is realized with division of the area of one pixel into plural areas for respective lights of colors; according to the field-sequential method, a desired color is realized with division of the display period into plural display periods for respective lights of colors.
The liquid crystal display device in which images are displayed by a field sequential method has the following advantages over the liquid crystal display device in which images are displayed by a color filter method. First, in the liquid crystal display device employing a field sequential method, it is not necessary to provide subpixels in a pixel. Thus, the aperture ratio can be improved or the number of pixels can be increased. In addition, in the liquid crystal display device employing a field sequential method, it is not necessary to provide a color filter. That is, loss of light due to light absorption in the color filter does not occur. Therefore, transmittance can be improved and power consumption can be reduced.
Patent Document 1 discloses a liquid crystal display device in which images are displayed by a field sequential method. Specifically, Patent Document 1 discloses a liquid crystal display device in which pixels each include a transistor for controlling input of an image signal, a signal storage capacitor for holding the image signal, and a transistor for controlling transfer of electric charge from the signal storage capacitor to a display pixel capacitor. In the liquid crystal display device having this structure, input of an image signal to the signal storage capacitor and display corresponding to electric charge held in the display pixel capacitor can be performed at the same time.
Patent Document 2 discloses a liquid crystal display device in which power consumed by a light source of a backlight (also referred to as a backlight source) can be reduced. Specifically, Patent Document 2 discloses a liquid crystal display device which includes a maximum value detection circuit which detects each of maximum values of color tones for R, G, and B in one screen (one field) and a backlight source which emits light of colors of R, G, and B in accordance with image signals so that the light of the emission colors does not overlap with each other.
In the above liquid crystal display device, a pixel for displaying a color tone having the highest brightness detected by the maximum value detection circuit has the highest aperture ratio (or the highest liquid crystal deflection angle), and display for this pixel is performed by control of brightness of the backlight source in accordance with the detected color tone having the highest brightness. Further, the aperture ratio (of liquid crystal deflection angle) of another pixel for displaying another color tone is controlled in accordance with a difference with the color tone having the highest brightness. In one screen (one field), the backlight source is operated in accordance with brightness of the color tone having the highest brightness of each of colors of R, G, and B, whereby power consumption can be reduced.